BUG#24855 - Crash mysqld 4.1.21 with corrupted tables

Accessing fixed record format table with crashed key definition results
in server/myisamchk segmentation fault.

This is fixed by refusing to open such tables. Affects MyISAM only.
No test case, since it requires crashed table.

myisam/mi_open.c

@@ -315,7 +315,13 @@ MI_INFO *mi_open(const char *name, int mode, uint open_flags)
 	for (j=0 ; j < share->keyinfo[i].keysegs; j++,pos++)
 	{
 	  disk_pos=mi_keyseg_read(disk_pos, pos);
-
+          if (pos->flag & HA_BLOB_PART &&
+              ! (share->options & (HA_OPTION_COMPRESS_RECORD |
+                                   HA_OPTION_PACK_RECORD)))
+          {
+            my_errno= HA_ERR_CRASHED;
+            goto err;
+          }
 	  if (pos->type == HA_KEYTYPE_TEXT || pos->type == HA_KEYTYPE_VARTEXT)
 	  {
 	    if (!pos->language)